The best laid plans of mice and men…

Entries Tagged as 'DOCSIS'

Several of my friends have ask for help on a very similar problem — they disconnect a computer directly from a cable modem or DSL router, plug in a residential gateway (wireless or wired router) and can’t get reconnected to the internet.

It’s actually a very common problem; and there are several things that can contribute to it.

The first thing you should do is make sure you that have the newest firmware available for your device — particularly older routers have issues with DHCP (that’s how most of the devices get the connection information from the service provider).

Also, you’ll want to check your computer to make sure what type of connection you were using to get to the internet (some older DSL modems particularly required that you setup your computer to do PPPoE — most newer DSL modems will handle all of that transparently, but even they may not be setup that way).

But after you check all that you’re still likely to find that you simply cannot make a connection to the internet.

The problem is that the internet service provider setup the profile of your modem so that it will only allow a single device to connect to the internet at a time (the MAC address to DHCP table has a limit of one). Each Ethernet device in the “universe” is supposed to have a unique MAC address; and the specification allows for what’s called locally administered MAC addresses as well, but no two devices should ever have the same permanent MAC address (and technically no device should be allowed to copy the permanent MAC address of another).

There are two ways to get around this. One is to use the MAC address cloning feature of your router (that’s long term a HORRIBLE idea — it violates the rule that no two devices should have [or use] the same permanent MAC address; and the only advantage to it is that it might provide instant gratification). The second, and better, way is to simply allow your modem time to reset — and you can hasten that by unplugging the power from it and letting it sit for about ten minutes.

There is potentially another way to hasten the re-binding of a new MAC address to the modem. Some modems have a hardware reset button — but you’ll have to check the manual to see how to use it. Most modems also have a web interface and resetting the device is one of the options.

Most cable modems have the ip address of 192.168.100.1, most ADSL modems have the address of 192.168.1.1, and VDSL modems have the address of 192.168.1.254 — but let me underscore I said most, not all (you’re going to have to read the manual if these don’t work — and to make it worse, some inexpensive modems have no web interface at all).

Once you bring up a web browser and point it to http://192.168.1.254/ (or what ever the address for your modem is) you’ll probably be able to just view much of the information with any authentication (and you need not have an internet connection for this to work). However, to reset the modem (or possible run diagnostics) you probably will need to log in. Many ADSL and VDSL modems will simply want you to enter the information printed on the modem (that’s to prevent a hacker from doing it, since it require physical access to the equipment), but again, you really will have to review the manual to be sure.

The option you’re looking for will be called something like “reset: or “restart”… and there should be a warning that the internet connection will be interrupted, and that it will take several minutes (worst case) for the connection to be re-established.

If all this sounds like too much work; there is a third way, and that just involves patience. The MAC address from the old device connected directly to your modem will age out over time — you just have to wait for it to happen (and it could be a hour or more). If it’s late at night, just hit the sack, and when you wakeup the next day everything should be working with your new residential gateway.

Also, many service providers offer a wireless residential gateway (with built in modem) in place of just the modem — for most residential users just selecting that instead of the modem makes sense… for “power users” you might want a router that has more features or better performance; but the service providers residential gateway, out of the box, will allow you to connect as many devices as you’d like (including another gateway if you like — just make sure the ip network addresses they use are different).

DOCSIS is used by most cable companies, and technically it’s not a cable modem, but a DOCSIS “cable” modem.

SDSL isn’t used much in the US any longer, so it’s unlikely you’re going to find one of these modems.

ADSL is used by most of the Telcos, including AT&T and Verizon.

VDSL (ADSL2+) is used by AT&T in their U-Verse service and Verizon in their FiOS service.